1. Field of the Invention
The present invention relates to an improved torque limiting coil clutch and in particular to a torque limiting coil clutch connection which will limit torque transmission in each direction of rotation by slipping at a clutch surface or interface at which torque is transmitted in the low torque transfer capacity direction of rotation for that interface and to automatic clearance sensing slack adjusters utilizing same.
2. Description of the Prior Art
Torque limiting coil clutches utilized to provide a limited torque rotational connection between a rotary driving and driven member are well known in the prior art as may be seen by reference to U.S. Pat. Nos. 3,727,732 and 4,280,606, the disclosures of which are hereby incorporated by reference. Briefly, in devices of this type the coil clutch is selected to slip at torque valves above a predetermined maximum.
Automatic slack adjusters of the single acting clearance or force sensing type, usually utilized to adjust vehicle brakes to compensate for friction lining wear, are well known in the prior art as may be seen by reference to U.S. Pat. Nos. 3,507,369; 3,901,357; 3,997,035 and 4,235,312, the disclosures of which are hereby incorporated by reference. These devices typically utilize a so called "one-way" helical coil clutch to limit torque applied to the brake adjustment member in the clearance or slack takeup, i.e. slack decreasing, direction of rotation. While such clutches are often referred to as one-way clutches as they are effective to rotate the driven member in only one direction against the system resistance to rotation, they are actually two-way devices having a relatively higher and a relatively lower maximum torque transfer capacity direction of rotation. In single acting adjusters of this type, it is important that a separate true one-way connection be provided, or that the torque transfer capacity of the coil clutch in the backoff direction of rotation be relatively small i.e. (smaller than system resistance to rotation of the adjuster member in the backoff or slack increasing direction of rotation) to prevent unwanted backoff of the slack adjuster.
Automatic clearance sensing slack adjusters wherein the torque limiting coil clutch will slip in the low torque transfer direction of rotation while rotating the adjustment member in the slack decreasing direction of rotation are known as may be seen by reference to U.S. Pat. No. 4,351,419, the disclosure of which is hereby incorporated by reference. By slipping in the low torque transfer capacity direction of rotation, the clutch slip torque is less sensitive to variations in coefficient of friction between the coil clutch and the surfaces of the driving and driven members engaged thereby. It is noted that relatively large variations in the coefficient of friction between the coil clutch and the surfaces engaged thereby may occur upon wear, loss of lubrication and the like.
While the prior art torque limiting coil clutches, and the clearance sensing single acting automatic slack adjusters utilizing same, are relatively acceptable, the devices are not totally satisfactory as the clutches do not slip in the low torque transfer capacity direction of rotation for the interface surface in both directions of rotation and thus automatic slack adjusters utilizing same may be sensitive to variations of or changes in coefficient of friction in the high torque transfer direction of rotation and/or require an additional one-way coupling, such as an additional coil clutch, ratchet, sprague clutch or the like.